Kefalonia, also known as Cephallenia, Cephallonia, Kefallinia, or Kefallonia (Ancient Greek: Κεφαλληνία; Modern Greek: Κεφαλλονιά or Κεφαλονιά), is the largest of the Ionian Islands in western Greece with an area of 350 sq. miles. Location: 20°30' E, and between 38°12' and 38°18' N.

The island is named after the mythological figure Cephalus (Ciphalis), although some believe its name literally means "an island with a head", referring to the island's shape, because the name "Ciphalis" is derived from the Greek word for "head".

The capital of the Kefalonia prefecture is Argostoli. The island's population is nearly 45,000. It used to be the fastest-growing part of Greece, with a growth rate of 35% to 40% during the 1990s. The size of the island is ca. 800 km² (300 mi²), and the present population density is 55 people per km² (140/mi²). Argostoli is home to one-third of the island's habitants. Lixouri is the second major settlement. The two towns account for almost two-thirds of the prefecture's population.

In ancient times, before it was named Kefalonia, only around 100 to 300 people lived there. When Kefalonia was founded in ancient times, the population had trebled to around 500–1,000 people. The population steadily grew until it reached 10,000 in the mid-20th century. The total topped 20,000 during the 1970s.

The island is covered by dense vegetation and offers plentiful natural beauty including beaches -- many of them inaccessible from land -- and spectacular caves. Mirtos, the most famous of these beaches, is a major tourist attraction, and has been ranked fifth worldwide for its scenic view.

Kefalonia's tallest mountain is Mount Ainos, elevation of 1628m (almost the same elevation as Denver, Colorado in North America). To the west-northwest are the Paliki mountains, where Lixouri is located. Other mountains include Gerania and Agia Dynati.

There are five harbours and ports in the prefecture: four main harbours on the island, Same or Sami, and a major port with links to Patras and Ithaca. Poros, in the south, has ferry routes to Kyllini. Argostoli, in the west, is the largest port, for local boats and ferries to Zante and regularly to Lixouri. Vasiliki, in the north, has links to Lefkas and Ithaca. There is room for about 100 small boats in Argostoli, where the port stretches 1 kilometre around the bay. Lixouri is situated 4 km across the bay from Argostoli, on the Lixouri peninsula. There is a road connection to the rest of the island, but driving from Lixouri to Argostoli involves a 30 km detour.

Kefalonia has one airport, Kephallinia Airport, with a runway of around 2.4 km. in length. The airport is about 10 km south of Argostoli. Almost every scheduled flight is an Olympic plane. The planes mainly fly to Athens, however there is an Ionian Island Hopper service 3 times a week calling at Kefalonia, Zante and Lefkas. In summer the airport handles many charter flights from all over Europe.

Kefalonia is located in the heart of an earthquake zone. Dozens of minor tremors occur each year. In 1953, a massive earthquake almost destroyed the island, leaving only Fiscardo in the north untouched.

Most of the Kefalonia population have surnames ending in "-atos".

A large number of tourists visit Kefalonia during the peak season but, as one of the largest islands in Greece, it is well-equipped to handle them. Most tourists stay in or around Lassi, a serene resort a few kilometres from Argostoli, and their numbers have increased since the best-seller, Captain Corelli's Mandolin, became a movie (2001) shot on the island itself.

Almost every community in Kefalonia has a name ending in "-ata", such as Lourdata, Favata, Delaportata, etc.

Kefalonia is home to two large monasteries. One is Haghia Panagia, in Markopoulo to the southeast, and the other is on the road between Argostoli and Michata, on a small plain surrounded by mountains. This second monastery has an avenue of about 200 trees lined from NW to SE with a circle in the middle. This is the monastery of Agios Gerasimos, who is the patron saint of the island.

A spectacular view of the Ionian Sea meeting the Agean Sea can be seen from west of Skála to north of Fiskárdo...